The increasing development of the modern all-optical information processing technology lays a solid foundation for the realization of optical circuit integrated chips. In 1987, E. Yablonovitch and S. John proposed the concept of photonic crystal. Later, photonic crystal is subjected to in-depth study continually and considered as one of the most potential photonic devices for realizing a new generation of all-optical integrated chips. Photonic crystal is a novel artificial material which is formed by the periodic arrangement of dielectric materials in space. Just like the fact that semiconductor materials can manipulate electrons, photonic crystal can control and operate photons as well. After 20 years' development, significant progress has been made in the aspects of the design and fabrication of photonic crystals. For example, high-performance optical reflectors, high-efficiency optical waveguides, ultra-narrow-band filters, highly-monochromatic lasers, fast all-optical switches and other optical devices, based on the photonic crystal structures. Photonic crystal devices have superior performances and small size, can be easily integrated with silicon-based materials in semiconductors, and have important application value in an all-optical information network.
Photonic crystal logic device has been a remarkable research hotspot in recent years and is highly likely to replace the currently widely used electronic logic devices in the near future. Photonic crystal logic functional devices such as “AND”, “OR”, “NOT” and “XOR” have been successfully designed, having the advantages of compact in structure, fast in arithmetic speed, capable of parallel operation, simplicity, etc., and being the basic elements for realizing all-optical logic operation. People are currently trying to explore the construction and optimization of more complex optical logic circuits such as photonic crystal comparators, photonic crystal A/D (D/A) converters and photonic crystal pulse generators. With the increase of the integration scale of the logic devices, the problem of mutual interference among components in an optical circuit has become more apparent. If this problem is not properly solved, the overall performances of the designed optical circuit can be greatly degraded, and normal logic functions cannot be even completed under severe cases. Magneto-optical circulator with non-reciprocity is a highly effective element for solving the problem as the magneto-optical circulator can realize low-loss transmission of light signals in the positive direction and high isolation of light signals in the opposite direction, can reduce optical crosstalk, and can improve the stability in signal transmission, thereby guaranteeing the normal operation of an optical integrated circuit system. However, being mainly based on bulky magneto-optical materials, the traditional magneto-optical circulator has large volume and thus is not suitable to be integrated with photonic crystal devices.